Cerebrospinal alterations of immunoreactive dynorphin A after unilateral dorsal rhizotomy in the rat

Possible alterations of immunoreactive dynorphin A (ir-dyn A) were investigated at different levels of the spinal cord and in discrete brain regions of male rats 10, 30 and 60 days after unilateral dorsal rhizotomy, i.e., during the development of deafferentation pain and autotomy behavior that follows afferent nerve interruption. Dorsal rhizotomy caused an increase of spinal ir-dyn A at 10 days in the cervical segment; subsequent assays showed a progressive increase in other spinal regions too. At the last observation, 60 days after rhizotomy, neuropeptide levels were still significantly higher than in sham-lesioned animals in the cervical, thoracic and lumbosacral spinal cord. The spinal ir-dyn A changes were both ipsi- and contralateral to the lesion. No alterations were found in the brainstem and midbrain and a not significant decrease was observed in the hypothalamus. In the striatum and cortex, however, there was a bilateral significant increase 30 days after surgery and a constant and significant elevation was detected in the hippocampus at all three intervals. These data cast additional light on the neurochemical changes caused by the interruption of afferent nerves, followed by development of the deafferentation pain syndrome in laboratory animals and human beings. They also support the concept of central neuroplasticity in pathological pain and indicate that the opioid neuropeptide dynorphin is involved.